The present invention relates to the field of gates, and more particularly to the field of cantilivered sliding gates.
Gates, of course, have been known since extremely ancient times, but few advances in their basic design have been made. A primary effort has been directed toward reducing the space that must be allocated for the typical swinging gate. A first-order solution to that problem substitutes a sliding member for the conventional swinging member, but a difficulty immediately arises in supporting the sliding member. Overhead support is only suitable when an overhead obstruction is permissible; clearly, roadways and the like where vehicles will pass are not amenable to this solution. Support from below also is possible, either by a track mechanism or a gate-mounted roller, but uneven surfaces and the possibility of obstructions, such as ice and snow, subtract from the utility of that approach.
As early as the beginning of this century, it was proposed to cantilever a gate across an opening, permitting a sliding gate, able to span a gap yet not requiring support either from above or below. U.S. Pat. No. 1,020,488, to Friend, discloses the basic design for such a concept. There, it can be seen that two vertical supports are provided, one immediately adjacent the gap and another spaced a distance away from it, with the gate being mounted to slide in a plane defined by the two vertical supports. The most important problem associated with cantilever structures, i.e., preventing downward deflection or sag in the far end of the cantilever beam, is addressed by a guy wire assembly. A prior reference to Anderson, U.S. Pat. No. 920,810, discloses much the same construction but without the guy wire assembly. Even so, the disclosure states that the assembly would sag but for provision of a triangular brace structure which absorbs much of the stress transmitted through the structural members. In both disclosures, the structural members are preferably iron pipe.
Over the years, improvements have been presented that eliminate some of the operational problems of this type device. For example, a significant problem relates to the use of exposed rollers as means for allowing the gate to slide. Such devices are highly susceptible to adverse weather conditions, particularly ice and snow, and over time they tend to become clogged with dirt and debris, degrading their movement. Also, they tend to move out of alignment over time, further impeding the easy movement of the gate. A solution to that problem was included in U.S. Pat. No. 3,531,895, which disclosed a vertical gate including a slide assembly riding in an enclosed track on the gate member. Also, U.S. Pat. No. 4,336,670, to Brutosky, suggested a telescoping mechanism that obviated the need for a "counterweight" section of the gate extending beyond the secondary support post when the gate was in the retracted position.
Notwithstanding these improvements, however, significant problems remain in this field. Primarily, such gates normally are constructed as single-piece units. That is, the upper and lower transverse members are fabricated as single pieces of tubular steel or aluminum. Thus, state-of-the-art devices, such as produced by the Anchor Post Company, of Baltimore, Md., and International Gate Devices, Inc., of Folsom, Pa., all see the necessity of long, relatively heavy transverse members to cope with the stress inherent in a cantilever device. The disadvantages of this approach are manifest. For example, such long, cumbersome structures are difficult and expensive to transport. Further, they require special care in installation, and if damaged, they cannot be repaired easily in the field.
Moreover, another serious problem appears when one attempts to construct such a wide gate, in that the downward-directed forces result in a twisting moment, producing a camber at the end of the gate. The art's only solution to this problem has been to add stiffening materials to the gate, exacerbating the weight, installation and transportation problems. Indeed, for relatively wide gates, the only solution has been to construct the gate in a so-called "box-spring" design, employing two complete gate structures in a side-by-side structure, connected by struts.
Thus, the time is ripe for a new approach to this problem, one that allows for ease of use and maintenance, without sacrificing stability.